Art Terms Glossary beginning with X

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An examination technique which uses x-rays (high-energy radiation with very short wavelengths -0.001 - 10 nm) to penetrate an artwork and expose photographic film. The depth of penetration depends on the material's density. X-rays are commonly used in museums to photograph density variations resulting from manufacture or restoration. For instance, a painting's structure can be better understood by showing the build-up of the pigments below the surface by virtue of their different densities. Repairs that are not apparent to the eye are often clearly visible in x-rays because of the differing densities of original materials versus restoration materials. X-rays also are used in analytical equipment (see x-ray diffraction and x-ray fluorescence) for the determination of molecular and elemental compositions.
X-ray diffraction
An examination technique used to identify the components of a solid crystalline material using an x-ray beam with a specified energy. The beam is transmitted or reflected through a sample in the form of a single crystal or crushed powder that diffracts it at varying angles dependent on the crystalline structures represented in the sample. The pattern of the diffracted beam is analyzed and used to determine the arrangement of the atoms in the material and obtain measurements of the spaces between atoms. This atomic arrangement is specific to each crystalline compound often enabling precise identification
X-ray fluorescence
Is a nondestructive analytical method used to qualitatively and/or quantitatively determine the element content of the materials.examined. An x-ray beam with a specific energy is generated by an x-ray tube. This beam excites the electrons causing them to momentarily jump to higher energy states. An energy burst characteristic for each element is emitted (fluorescence) when the electrons return to their original state. The x-ray spectrum emitted from each element has a unique set of energies that are related to the type and amount of atoms present in the sample. This energy emission is analyzed qualitatively to provide identifications of the elements present in the material. Quantitative analysis enables the composition of the material (the percentage of each reported element) to be determined. Detection limits vary depending on the instrument, sample matrix, and individual elements. Typically, for nondestructive XRF (operated in air rather than under vacuum) calcium is the lowest atomic number element that can be accurately measured.
A medical radiography technique formerly used to obtain mammograms. It has since proven useful in the study of ancient technology, particularly ceramics, because of its ability to enhance edge differences between masses rather than just documenting differences in radiodensity as does traditional x-radiography. Therefore, it enables us to see the way the clay has been built up and manipulated by the artist during construction.